Impact Melt Channel

Impact melt, rock that is melted by the tremendous energy released during an impact cratering
event, results in fascinating morphologies visible in many NAC images. Most melt stays inside
the crater, freezing into melt-ponds, but some is thrown out of the crater and flows down the
exterior ejecta blanket until it is completely solidified by surface cooling.

Today’s Featured Image explores a fantastic impact melt deposit on the southern rim slope of
Petavius B, about 2.5 km away from the rim. The flat floored arc-shaped area at the bottom of
this image was likely a pool of melt that drained out of the channel at the top. The shadows
highlight the depth and steep banks of the channel.

Similar morphologies are found within terrestrial lava flows, but the terrestrial examples often
have distinctive cracks as lava backs up beneath a crust forming tumuli or pressure ridges. Why
do we not see similar structures on the Moon? This is a mystery, but perhaps the impact melts
have lower viscosities or different cooling processes than the lava on Earth!